2) We often use radio-isotopes to estimate the age of things (such as the
Earth). Assuming the half-life of some isotope is 1000 years, and you
found a rock of unknown age near the Mid Atlantic Ridge. You measured
the amount of isotope in the rock and determined that 12.5% of the
original amount when the rock formed was still present. How old is the
rock

great. now, sometimes growth and decay have been modeled by exponential functions. This is the model common model and the one you'll be using here.
Do you know the form of the exponential function that is used to model growth and decay? is so, type it in here...